Many catalysts containing a nickel compound are known to oligomerize ethylene to higher olefins. For example, U.S. Pat. No. 4,482,640 discloses a process for the oligomerization of ethylene using a homogeneous catalyst consisting essentially of a nickel compound, a phosphine compound, and an acid; U.S. Pat. No. 3,647,915 discloses an ethylene oligomerization catalyst comprising an atom of nickel chelated with a chelating ligand having a tertiary organophosphine moiety and a carbonyl ligand; and U.S. Pat. No. 3,644,564 discloses ethylene oligomerization in the presence of a catalyst comprising nickel(0) complexed with a fluorine-containing ligand.
While the catalyst systems discussed above are operable for ethylene oligomerization, they are either homogeneous catalyst systems that are not suitable for continuous processes or relatively expensive. Additionally, some of the known ethylene oligomerization processes require long reaction time, high temperature, or both, to achieve satisfactory results. Furthermore, by using a known ethylene oligomerization process, one has not always achieved high catalyst productivity and good product selectivity. Finally, because of the increasing importance of higher olefins in chemical industries, for example, 1-butene as industrial feedstock, 1-hexene as comonomer for polyethylenes production, and 1-decene as comonomer for high temperature polyolefins, processes and catalysts that make even slight improvements in the availability of these olefins over the known processes and catalysts are highly desirable.